impedancepH

Impedance-pH monitoring, also known as multichannel intraluminal impedance-pH (MII-pH) monitoring, is a diagnostic technique used to evaluate gastroesophageal reflux disease (GERD) by measuring both impedance and pH in the esophagus. It detects reflux episodes based on changes in electrical impedance that occur when a bolus moves within the esophagus, and it simultaneously records the pH to determine the acidity of the refluxate. By integrating these data, clinicians can identify acid, weakly acid, and nonacid reflux events and assess their proximal extent and frequency.

The test is performed with a thin catheter that contains multiple impedance sensors along its length and a distal pH sensor near the lower esophageal sphincter. The catheter is placed transnasally and connected to a data logger. The patient goes about normal activities for about 24 hours, recording symptoms, meals, and posture. In some cases, a wireless pH monitor may be used as an alternative. Impedance-pH monitoring provides a more comprehensive assessment of reflux than pH monitoring alone because it captures nonacid reflux and reflux that does not reach the distal esophagus.

Indications include evaluation of GERD symptoms that persist despite therapy with acid suppression, uncertain symptom-reflux correlation, preoperative assessment for anti-reflux surgery, and pediatric investigations. Interpretation involves metrics such as the number of reflux episodes, acid exposure time, proximal extent of reflux, and symptom association measures (for example, SAP or SI). Limitations include patient discomfort, potential technical issues, and the need for expert interpretation, with threshold values varying by guideline and population.